EPDM membranes are used as a single ply roofing material for industrial and commercial flat roofs. Such membranes are generally applied to the roof surface in a vulcanized or cured state. Because of outstanding weather resistance and flexibility, cured EPDM roofing membrane material has rapidly gained acceptance. The material is typically prepared by vulcanizing the composition in the presence of sulfur or sulfur containing compounds such as mercaptans or by using radiation cross linking promoters in the EPDM material which can be cured by ionizing radiation, for example, see U.S. Pat. No. 4,803,020, incorporated herein by reference.
Notwithstanding the usefulness of radiation curing and sulfur curing of a sheet of EPDM, a disadvantage of utilizing EPDM material is the lack of adhesion of cured EPDM to itself. Accordingly, it is usually necessary to splice the cured EPDM roofing membranes together with an adhesive to bond the cured EPDM membranes together to form a continuous EPDM membrane to cover the roof. It will be appreciated that the use of an adhesive for splicing cured EPDM membranes together requires that the adhesive and the resulting bond must meet a number of requirements which are extremely difficult to satisfy. The adhesive must provide sufficient seam peel and shear strength to permit the splice formed by bonding the cured EPDM membranes together to resist both the short-term and long-term stresses experienced by the spliced EPDM roofing membrane.
In view of the foregoing, it is an object of the present invention to provide a method and apparatus for selectively curing only the field of a sheet of EPDM. It is another object of the present invention to provide a method and apparatus for selectively curing only the field of a sheet of EPDM with radiation, preferably infrared radiation, and to a method of joining at least two selectively cured EPDM membranes to form a larger membrane. Yet another object of the present invention is to provide a method of splicing selectively cured EPDM membranes having a cured field and uncured longitudinal edge area which eliminates the need for a solvent based or non-solvent based splicing adhesive along the overlapping edge area and the related labor and hardware necessary for mixing and application thereof. It is another object of the present invention to provide a method and apparatus for curing only the field of a sheet of EPDM that is simple and economical.